The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Continuously variable transmissions (CVT's) provide exceptional torque and speed engine and load matching. Because of this inherent feature, and because of the ever increasing emphasis on fuel economy, they have become correspondingly popular, especially in lower horsepower vehicles intended for the mass market.
Accordingly, significant engineering effort has been directed to this transmission type in recent years to optimize performance, efficiency and ruggedness while reducing weight and complexity. Not only is development effort directed to the continuously variable portion of the transmission, i.e., a twin pulley and belt arrangement or a variator, but also to the associated components which provide forward and reverse and multiple modes (speed ranges) inasmuch as these components also significantly impact fuel economy and performance.
Specifically, a vast majority of automatic transmissions, both planetary gear types and continuously variable types, utilize friction pack clutches and brakes. While these devices are capable of transmitting significant torque through a relatively small package, because they comprise first and second pluralities of interleaved plates or discs, one plurality of which will typically be rotating and the other stationary when the device is not engaged, they generate spin losses—losses which may be of significant magnitude if the speed difference across the device is great. Hence, minimizing the number of friction pack clutches and brakes is, in itself, an approach to improving transmission efficiency.